Casting powders have been provided heretofore for the casting of steel, especially high-alloy steel (i.e. steel containing aluminum or titanium) and for continuous casting from silicon dioxide, aluminum oxide, calcium oxide, magnesium oxide, sodium oxide, potassium oxide and fluxing agents generally of the borate or fluoride type.
Casting powders of these kinds are used to increase the purity of the cast article, e.g. ingots or bars, blooms or the like, which are to be further worked, e.g. by rolling. They also improve the solidification characteristics of the cast materials and produce cast articles with especially fine surface properties. The casting powders with which the invention is concerned are not, however, confined to mold-lining powders for poured castings of the single-unit type but may be used for the casting of alloy steels, especially aluminum and titanium containing steels in such static molds as well as continuous-casting molds in which the product is a continuous ingot.
The casting powder used conventionally may contain a fluxing agent, hereinafter referred to generally as a flux, which contributes to improving the wetting characteristics of the slag formed during the process and reduces the melting point thereof, and modifies the viscosity.
In conventional systems the flux is a fluoride or borate, especially calcium floride (e.g. fluorspar) or sodium tetraborate decahydrate (borax). The use of fluorides and borates as fluxing agents in casting powder is not, however, free from disadvantages. For example, the use of fluorides as a fluxing agent in casting powders results in thermal decomposition of the fluxing agent to produce gaseous fluorine which is toxic and cannot be tolerated where environmental pollution is to be minimized. The use of borates as a fluxing agent may result in a cast article having a high concentration of boron in surface regions which modifies the structural characteristics of the cast article.